Existing conventional megajoule plasma focus machines with 2–3 MA are producing fusion neutron yields of several times 10^(11) in deuterium operation,the fusion yields predominantly being the beam-gas target.Increasi...Existing conventional megajoule plasma focus machines with 2–3 MA are producing fusion neutron yields of several times 10^(11) in deuterium operation,the fusion yields predominantly being the beam-gas target.Increasing the current to 10 MA and using 50%–50%D-T mixture will scale the neutron yield towards 10^(16) D-T fusion neutrons.In this work,we derive the Lawson criterion for plasma focus devices with a beam-target fusion neutron mechanism,so that we may glimpse what future technological advancements are needed for a break-even Q=1 plasma focus.We perform numerical experiments with a present-day feasible 0.9 MV,8.1 MJ,11 MA machine operating in 100 Torr in 50%–50%D-T mixture.The Lee Code simulation gives a detailed description of the plasma focus dynamics through each phase,and provides plasma and yield parameters which show that out of 1.1×10^(19) fast beam ions produced in the plasma focus pinch,only 1.24×10^(14) ions take part in beam-target fusion reactions within the pinch,producing the same number of D-T neutrons.The remnant beam ions,numbering at least 10^(19),exit the focus pinch at 1.9 MeV,which is far above the 115 keV ion energy necessary for an optimum beam-target cross-section.We propose to regain the lost fusion rates by using a high-pressure D-T-filled drift-tube to attenuate the energy of the remnant beam ions until they reach the energy for the optimum fusion cross-section.Such a fusion enhancement tube would further harvest beam-target fusion reactions by increasing the interaction path length(1 m)at increased interaction density(6 atm).A gain factor of 300 is conservatively estimated,with a final yield of 3.7×10^(16) D-T neutrons carrying kinetic energy of 83.6 kJ,demonstrating Q=0.01.展开更多
The paper describes the operation features of plasma focus chambers using deuteriumetritium mixture.Handling tritium requires the use of sealed,vacuum-tight plasma focus chambers.In these chambers,there is an accumula...The paper describes the operation features of plasma focus chambers using deuteriumetritium mixture.Handling tritium requires the use of sealed,vacuum-tight plasma focus chambers.In these chambers,there is an accumulation of the impurity gases released from the inside surfaces of the electrodes and the insulator while moving plasma current sheath inside chambers interacting with b-electrons generated due to the decay of tritium.Decay of tritium is also accompanied by the accumulation of helium.Impurities lead to a decreased yield of neutron emission from plasma focus chambers,especially for long term operation.The paper presents an option of absorption type gas generator in the chamber based on porous titanium,which allows to significantly increase the lifetime and shelf life of tritium chambers.It also shows the results of experiments on the comparison of the operation of sealed plasma focus chambers with and without the gas generator.展开更多
The multi-radiation of X-rays was investigated with special attention to their energy spectrum in a Mather-type plasma focus device （operated with argon gas）. The analysis is based on the effect of anomalous resista...The multi-radiation of X-rays was investigated with special attention to their energy spectrum in a Mather-type plasma focus device （operated with argon gas）. The analysis is based on the effect of anomalous resistances. To study the energy spectrum, a four-channel diode X-ray spectrometer was used along with a special set of filters. The filters were suitable for detection of medium range X-rays as well as hard X-rays with energy exceeding 30 keV. The results indicate that the anomalous resistivity effect during the post pinch phase may cause multi-radiation of X-rays with a total duration of 300 ± 50 ns. The significant contribution of Cu-Kα was due to the medium range X-rays, nonetheless, hard X-rays with energies greater than 15 keV also participate in the process. The total emitted X-ray energy in the forms of Cu-K and Cu-K/3 was around 0.14 ± 0.02 （J/Sr） and 0.04 ±0.01 （J/Sr）, respectively. The total energy of the emitted hard X-ray （〉 15 keV） was around 0.12± 0.02 （J/Sr）.展开更多
In the experiment to determine the plasma electron temperature, a modifiedmultichannel PIN diodes assembly is used as detectors to record the X-ray pulses from a low-energyMather-type plasma focus device energized by ...In the experiment to determine the plasma electron temperature, a modifiedmultichannel PIN diodes assembly is used as detectors to record the X-ray pulses from a low-energyMather-type plasma focus device energized by a 32μF, 15 kV (3.6kJ) single capacitor, with deuteriumas a filling gas. The ratio of the integrated bremsstrahlung emission transmitting through foils tothe total incident flux as a function of foil thickness at various temperatures is obtained forfoil absorbers of material. Using 3 μm, 6 μm, 9 μm,12 μm,15 μm and 18 μm thick aluminiumabsorbers, the transmitted X-ray flux is detected. By comparing the experimental and theoreticalcurves through a computer program, the plasma electron temperature is determined. Results show thatthe deuterium focus plasma electron temperature is about 800 eV.展开更多
The design details and performance characterization results of a newly developed plasma focus based compact and portable system(0.5 m×0.5 m×1.2 m,weighing≈100 kg)that produces an average neutron yield of^2&...The design details and performance characterization results of a newly developed plasma focus based compact and portable system(0.5 m×0.5 m×1.2 m,weighing≈100 kg)that produces an average neutron yield of^2×10^8 neutrons/shot(of fast D-D neutrons with typical energy^2.45 Me V)at^1.8 k J energy discharge are reported.From the detailed analysis of the experimental characterization and simulation results of this system,it has been conclusively revealed that specifically in plasma focus devices with larger static inductance:(i)pinch current is a reliable and more valid neutron yield scaling parameter than peak current,(ii)the ratio of pinch/peak current improves as static inductance of the system reduces,(iii)the benign role of the higher static/pinch inductance ratio enables the supply of inductively stored energy in densely pinched plasma with a larger time constant and it is well depicted by the extended dip observed in the discharge current trace,(iv)there is the need to redefine existing index values of the pinch(Ipinch^4.7)and peak(Ipeak^3.9)currents in neutron yield scaling equations to higher values.展开更多
We report a simple-to-perform technique to investigate the distribution of the azimuthal magnetic field induction,Bθ,and the induced magnetic force acting on the plasma current sheath(PCS)in a plasma focus(PF)dischar...We report a simple-to-perform technique to investigate the distribution of the azimuthal magnetic field induction,Bθ,and the induced magnetic force acting on the plasma current sheath(PCS)in a plasma focus(PF)discharge.This in situ measurement technique can undoubtedly be beneficial when other fast-imaging techniques are not available.techniques are not available.Experimental work was conducted in the low-energy Mather-type EAEA-PF1 device operated in argon.The axial distribution(Bθ)z along the coaxial electrodes system was measured with a four magnetic-probe set technique at different radial distances(r=2.625×10^(−2) to 4.125×10^(−2) m)within the annular space between the coaxial electrodes during the 1st and 2nd half cycles of the discharge current waveform,where inner electrode of coaxial electrode system has a+ve polarity and−ve polarity,respectively.Axial,radial and total magnetic force distribution profiles were estimated from Bθdata.Investigation of PCS shape in terms of its inclination(curvature)angle,θ,along the axial rundown phase and the correlation between the magnetic forces per unit volume acting on the PCS,the inclination angleθof the PCS,and the formation of a powerful PF action during the 1st and 2nd half cycles is carried out.Dependence of inclination angle,θ,on total magnetic force per unit volume acting on PCS axial motion was studied,separately,during the 1st and 2nd half cycles.展开更多
An indirect method is proposed for measuring the relative energy spectrum of the pulsed electron beam of a plasma focus device. The Bremsstrahlung x-ray, generated by the collision of electrons against the anode surfa...An indirect method is proposed for measuring the relative energy spectrum of the pulsed electron beam of a plasma focus device. The Bremsstrahlung x-ray, generated by the collision of electrons against the anode surface, was measured behind lead filters with various thicknesses using a radiographic film system. A matrix equation was considered in order to explain the relation between the x-ray dose and the spectral amplitudes of the electron beam. The electron spectrum of the device was measured at 0.6 mbar argon and 22 kV charging voltage, in four discrete energy intervals extending up to 500 keV. The results of the experiments show that most of the electrons are emitted in the 125-375 keV energy range and the spectral amplitude becomes negligible beyond 375 keV.展开更多
The Al/a-C nanocomposite thin films are synthesized on Si substrates using a dense plasma focus device with alu- minum fitted anode and operating with CH4/Ar admixture. X-ray diffractometer results confirm the formati...The Al/a-C nanocomposite thin films are synthesized on Si substrates using a dense plasma focus device with alu- minum fitted anode and operating with CH4/Ar admixture. X-ray diffractometer results confirm the formation of metallic crystalline Al phases using different numbers of focus shots. Raman analyses show the formation of D and G peaks for all thin film samples, confirming the presence of a-C in the nanocomposite thin films. The formation of Al/a-C nanocomposite thin films is further confirmed using X-ray photoelectron spectroscopy analysis. The scanning electron microscope results show that the deposited thin films consist of nanoparticles and their agglomerates. The sizes of th agglomerates increase with increasing numbers of focus deposition shots. The nanoindentation results show the variations in hardness and elastic modulus values of nanocomposite thin film with increasing the number of focus shots. Maximum values of hardness and elastic modulus of the composite thin film prepared using 20 focus shots are found to be about 10.7 GPa and 189.2 GPa, respectively.展开更多
Study on X-ray emission from a low energy (1.8 kJ) plasma focus devicepowered by a 9 μF capacitor bank, charged at 20 kV and giving peak discharge current of about 175kA by using a lead-inserted copper-tapered anode ...Study on X-ray emission from a low energy (1.8 kJ) plasma focus devicepowered by a 9 μF capacitor bank, charged at 20 kV and giving peak discharge current of about 175kA by using a lead-inserted copper-tapered anode is reported. The X-ray yield in different energywindows is measured as a function of hydrogen filling pressure. The maximum yield in 4π-geometry isfound to be (27.3+-1.1) J and corresponding wall plug efficiency for X-ray generation is 1.52+-0.06%. X-ray emission, presumably due to bombarding activity of electrons in current sheath at theanode tip was dominant, which is confirmed by the pinhole images. The feasibility of the device asan intense X-ray source for radiography is demonstrated.展开更多
The current sheath velocity in 0.25 Torr gas pressure of Filippov type plasma focus is studied experimentally. By using two tridimensional magnetic probes on top of the anode surface, the current sheath velocity is me...The current sheath velocity in 0.25 Torr gas pressure of Filippov type plasma focus is studied experimentally. By using two tridimensional magnetic probes on top of the anode surface, the current sheath velocity is measured for argon, oxygen and nitrogen. Additionally, the effect of charging voltage on the current sheath velocity is studied in both axial and radial phases. We found that, the maximum current sheath velocities at both radial and axial phases are respectively 4.33 ± 0.28 （cm/μs） and 3.92 ± 0.75 （cm/μs） with argon as the working gas at 17 kV. Also, the minimum values of current sheath velocity are 1.48 ± 0.15 （cm/μs） at the radial phase and 1.14 ± 0.09 （cm/μs） at the axial phase with oxygen at 12 kV. The current sheath velocity at the radial phase is higher than that at the axial phase for all gases and voltages. In this study, variation of the full width half maximum （FWHM） of magnetic probe signals with voltage is investigated for different gases at radial and axial phases.展开更多
A 2.3 kJ Mather type pulsed plasma focus device was used for the synthesis of a TiN/a-Si3N4 thin film at room temperature. The film was characterized using X-ray diffraction （XRD）, X-ray photoelectron spectroscopy ...A 2.3 kJ Mather type pulsed plasma focus device was used for the synthesis of a TiN/a-Si3N4 thin film at room temperature. The film was characterized using X-ray diffraction （XRD）, X-ray photoelectron spectroscopy （XPS）, scanning electron microscopy （SEM）, and atomic force microscopy （AFM）. The XRD pattern confirms the growth of polycrystalline TiN thin film. The XPS results indicate that the synthesized film is non-stoichiometric and contains titanium nitride, silicon nitride, and a phase of silicon oxy-nitride. The SEM and AFM results reveal that the surface of the synthesized film is quite smooth with 0.59 nm roughness （root-mean-square）.展开更多
A simple, low cost, easily maintained, and reliable field distortion spark gap has been developed to operate at a voltage up to 30 kV. The header construction necessary to attach the spark gap switch to a single 12.5 ...A simple, low cost, easily maintained, and reliable field distortion spark gap has been developed to operate at a voltage up to 30 kV. The header construction necessary to attach the spark gap switch to a single 12.5 μF, 40 kV （10 k J） capacitor is described. The main features of the spark gap are its wide range of voltage operation, high current capacity, low inductance and long lifetime. The performance of spark gap has been tested in a plasma focus and results are presented in this report.展开更多
The Al–C–N films are deposited on Si substrates by using a dense plasma focus（DPF） device with aluminum fitted central electrode（anode） and by operating the device with CH_4/N_2 gas admixture ratio of 1：1. XRD ...The Al–C–N films are deposited on Si substrates by using a dense plasma focus（DPF） device with aluminum fitted central electrode（anode） and by operating the device with CH_4/N_2 gas admixture ratio of 1：1. XRD results verify the crystalline Al N（111） and Al_3CON（110） phase formation of the films deposited using multiple shots. The elemental compositions as well as chemical states of the deposited Al–C–N films are studied using XPS analysis, which affirm Al–N, C–C, and C–N bonding. The FESEM analysis reveals that the deposited films are composed of nanoparticles and nanoparticle agglomerates. The size of the agglomerates increases at a higher number of focus deposition shots for multiple shot depositions. Nanoindentation results reveal the variation in mechanical properties（nanohardness and elastic modulus）of Al–C–N films deposited with multiple shots. The highest values of nanohardness and elastic modulus are found to be about 11 and 185 GPa, respectively, for the film deposited with 30 focus deposition shots. The mechanical properties of the films deposited using multiple shots are related to the Al content and C–N bonding.展开更多
Optimal condition for <sup>13</sup>N radioisotope production through <sup>12</sup>C (d,n) 13N within plasma focus device is investigated. As the deuteron spectrum follows the empirical power la...Optimal condition for <sup>13</sup>N radioisotope production through <sup>12</sup>C (d,n) 13N within plasma focus device is investigated. As the deuteron spectrum follows the empirical power law of the form E<sup>-m</sup>, it is shown that the activity decreases by increasing the value of m. Unlike the fact that the repetition rate increases the activity, it is possible to achieve higher activities by increasing the bombardment time at a fixed repetition rate.展开更多
In many experiments, plastic scintillators are used as a counter instead of Geiger Muller counter, because they are so fast and they are used for pulsed neutron sources. So a silver activation counter has been constru...In many experiments, plastic scintillators are used as a counter instead of Geiger Muller counter, because they are so fast and they are used for pulsed neutron sources. So a silver activation counter has been constructed by plastic scintillator plates along with silver foils for determination the neutron yield of a 2.48 kJ plasma focus device, SBUPF1. This counter was calibrated by source removal method with an Am-Be 5 Ci neutron source which was placed above the anode of plasma focus device. Deuterium gas up to 8 mbar pressure was injected to this device, and the neutron yield produced by pulsed D-D fusion of plasma focus device was measured by the counter. The neutron yield of SBUPF1 in 8 mbar pressure was obtained （3.71± 0.32）×10^7 neutrons per shot. This result has relatively agreed with the neutron yield measured by silver activation Geiger counters.展开更多
The plasma focus experiment in Belgrade, Serbia started in the late eighties of the last century. The historical overview of the research activity on the Belgrade plasma focus device (BPFD) will be presented in this w...The plasma focus experiment in Belgrade, Serbia started in the late eighties of the last century. The historical overview of the research activity on the Belgrade plasma focus device (BPFD) will be presented in this work. The special attention has been made to the present status and the future plans for the fundamental and applied research as a part of the project of the studies of rare nuclear and particle processes in nature. BPFD is intended to operate as optimized neutron source or hard X-ray source. Using Lee model code as a reference, several upgrades of BPFD must be made: better shielding against EMI pulse, rearrangement of capacitors bank so that higher repetition rate can be achieved and also faster digital acquisition system. BPFD can be used for neutron activation or production of short-living radioisotopes. These radioisotopes will have very low activity which can be analyzed in the underground Low-Background Laboratory for Nuclear Physics, Zemun. Also, we compared the obtained experimental data (neutron yield, total current waveform, working gas pressure) with the numerical simulation code (The Lee model code) to test our plasma focus machine. Comparison between neutron yield from our experimental data and neutron scaling laws and neutron yields derived from computation using the Lee Model code shows good matching, but for better verification of the code, more experimental data are needed.展开更多
In most collisional schemes of x-ray laser （XRL） experiments, a bow-like intensity distribution of XRL is often observed, and it is generally ascribed to the two-dimensional hydrodynamic behaviour of expanding plasm...In most collisional schemes of x-ray laser （XRL） experiments, a bow-like intensity distribution of XRL is often observed, and it is generally ascribed to the two-dimensional hydrodynamic behaviour of expanding plasma. In order to better understand its essence in physics, a newly developed two-dimensional non-equilibrium radiation hydrodynamic code XRL2D is used to simulate a quasi-steady state Ni-like Ag XRL experiment on ShenGuang-Ⅱfacility. The simulation results show that the bow-like distribution of Ni-like ions caused by over-ionization in the central area of plasma is responsible for the bow-like shape of the XRL intensity distribution observed.展开更多
The Max’s equation of self-focusing in laser-plasma interaction due to the pondermotive force has been discussed and its physical meaning of the assumption has been predicted. The characteristics of selffocusing due ...The Max’s equation of self-focusing in laser-plasma interaction due to the pondermotive force has been discussed and its physical meaning of the assumption has been predicted. The characteristics of selffocusing due to the pondermotive force with different initial situations have been analyzed through the numerical calculation.展开更多
Based on the two-dimensional model, this paper compares the hydrodynamics of slab x-ray laser plasma produced by different nonuniform line focused irradiations. It finds that the average intensity and the duration of ...Based on the two-dimensional model, this paper compares the hydrodynamics of slab x-ray laser plasma produced by different nonuniform line focused irradiations. It finds that the average intensity and the duration of laser pulse and the overall shape of the intensity distribution in the focal line have different influences on the plasma. Calculations show that the evolution of temperature variation is more sensitive to the pulse duration and the electron density variation is more sensitive to the pulse intensity. Pulses with duration of 200 ps to 500 ps and with intensity of 0.2 TW/cm2 to 1.0 TW/cm2 are proved acceptable in slab x-ray lasers.展开更多
文摘Existing conventional megajoule plasma focus machines with 2–3 MA are producing fusion neutron yields of several times 10^(11) in deuterium operation,the fusion yields predominantly being the beam-gas target.Increasing the current to 10 MA and using 50%–50%D-T mixture will scale the neutron yield towards 10^(16) D-T fusion neutrons.In this work,we derive the Lawson criterion for plasma focus devices with a beam-target fusion neutron mechanism,so that we may glimpse what future technological advancements are needed for a break-even Q=1 plasma focus.We perform numerical experiments with a present-day feasible 0.9 MV,8.1 MJ,11 MA machine operating in 100 Torr in 50%–50%D-T mixture.The Lee Code simulation gives a detailed description of the plasma focus dynamics through each phase,and provides plasma and yield parameters which show that out of 1.1×10^(19) fast beam ions produced in the plasma focus pinch,only 1.24×10^(14) ions take part in beam-target fusion reactions within the pinch,producing the same number of D-T neutrons.The remnant beam ions,numbering at least 10^(19),exit the focus pinch at 1.9 MeV,which is far above the 115 keV ion energy necessary for an optimum beam-target cross-section.We propose to regain the lost fusion rates by using a high-pressure D-T-filled drift-tube to attenuate the energy of the remnant beam ions until they reach the energy for the optimum fusion cross-section.Such a fusion enhancement tube would further harvest beam-target fusion reactions by increasing the interaction path length(1 m)at increased interaction density(6 atm).A gain factor of 300 is conservatively estimated,with a final yield of 3.7×10^(16) D-T neutrons carrying kinetic energy of 83.6 kJ,demonstrating Q=0.01.
文摘The paper describes the operation features of plasma focus chambers using deuteriumetritium mixture.Handling tritium requires the use of sealed,vacuum-tight plasma focus chambers.In these chambers,there is an accumulation of the impurity gases released from the inside surfaces of the electrodes and the insulator while moving plasma current sheath inside chambers interacting with b-electrons generated due to the decay of tritium.Decay of tritium is also accompanied by the accumulation of helium.Impurities lead to a decreased yield of neutron emission from plasma focus chambers,especially for long term operation.The paper presents an option of absorption type gas generator in the chamber based on porous titanium,which allows to significantly increase the lifetime and shelf life of tritium chambers.It also shows the results of experiments on the comparison of the operation of sealed plasma focus chambers with and without the gas generator.
文摘The multi-radiation of X-rays was investigated with special attention to their energy spectrum in a Mather-type plasma focus device （operated with argon gas）. The analysis is based on the effect of anomalous resistances. To study the energy spectrum, a four-channel diode X-ray spectrometer was used along with a special set of filters. The filters were suitable for detection of medium range X-rays as well as hard X-rays with energy exceeding 30 keV. The results indicate that the anomalous resistivity effect during the post pinch phase may cause multi-radiation of X-rays with a total duration of 300 ± 50 ns. The significant contribution of Cu-Kα was due to the medium range X-rays, nonetheless, hard X-rays with energies greater than 15 keV also participate in the process. The total emitted X-ray energy in the forms of Cu-K and Cu-K/3 was around 0.14 ± 0.02 （J/Sr） and 0.04 ±0.01 （J/Sr）, respectively. The total energy of the emitted hard X-ray （〉 15 keV） was around 0.12± 0.02 （J/Sr）.
基金This work was partially supported by Quaid-i-Azam University research Grant Pakistan Science Foundation Project Pakistan Atomic Energy Commission Project for Plasma Physics
文摘In the experiment to determine the plasma electron temperature, a modifiedmultichannel PIN diodes assembly is used as detectors to record the X-ray pulses from a low-energyMather-type plasma focus device energized by a 32μF, 15 kV (3.6kJ) single capacitor, with deuteriumas a filling gas. The ratio of the integrated bremsstrahlung emission transmitting through foils tothe total incident flux as a function of foil thickness at various temperatures is obtained forfoil absorbers of material. Using 3 μm, 6 μm, 9 μm,12 μm,15 μm and 18 μm thick aluminiumabsorbers, the transmitted X-ray flux is detected. By comparing the experimental and theoreticalcurves through a computer program, the plasma electron temperature is determined. Results show thatthe deuterium focus plasma electron temperature is about 800 eV.
文摘The design details and performance characterization results of a newly developed plasma focus based compact and portable system(0.5 m×0.5 m×1.2 m,weighing≈100 kg)that produces an average neutron yield of^2×10^8 neutrons/shot(of fast D-D neutrons with typical energy^2.45 Me V)at^1.8 k J energy discharge are reported.From the detailed analysis of the experimental characterization and simulation results of this system,it has been conclusively revealed that specifically in plasma focus devices with larger static inductance:(i)pinch current is a reliable and more valid neutron yield scaling parameter than peak current,(ii)the ratio of pinch/peak current improves as static inductance of the system reduces,(iii)the benign role of the higher static/pinch inductance ratio enables the supply of inductively stored energy in densely pinched plasma with a larger time constant and it is well depicted by the extended dip observed in the discharge current trace,(iv)there is the need to redefine existing index values of the pinch(Ipinch^4.7)and peak(Ipeak^3.9)currents in neutron yield scaling equations to higher values.
文摘We report a simple-to-perform technique to investigate the distribution of the azimuthal magnetic field induction,Bθ,and the induced magnetic force acting on the plasma current sheath(PCS)in a plasma focus(PF)discharge.This in situ measurement technique can undoubtedly be beneficial when other fast-imaging techniques are not available.techniques are not available.Experimental work was conducted in the low-energy Mather-type EAEA-PF1 device operated in argon.The axial distribution(Bθ)z along the coaxial electrodes system was measured with a four magnetic-probe set technique at different radial distances(r=2.625×10^(−2) to 4.125×10^(−2) m)within the annular space between the coaxial electrodes during the 1st and 2nd half cycles of the discharge current waveform,where inner electrode of coaxial electrode system has a+ve polarity and−ve polarity,respectively.Axial,radial and total magnetic force distribution profiles were estimated from Bθdata.Investigation of PCS shape in terms of its inclination(curvature)angle,θ,along the axial rundown phase and the correlation between the magnetic forces per unit volume acting on the PCS,the inclination angleθof the PCS,and the formation of a powerful PF action during the 1st and 2nd half cycles is carried out.Dependence of inclination angle,θ,on total magnetic force per unit volume acting on PCS axial motion was studied,separately,during the 1st and 2nd half cycles.
文摘An indirect method is proposed for measuring the relative energy spectrum of the pulsed electron beam of a plasma focus device. The Bremsstrahlung x-ray, generated by the collision of electrons against the anode surface, was measured behind lead filters with various thicknesses using a radiographic film system. A matrix equation was considered in order to explain the relation between the x-ray dose and the spectral amplitudes of the electron beam. The electron spectrum of the device was measured at 0.6 mbar argon and 22 kV charging voltage, in four discrete energy intervals extending up to 500 keV. The results of the experiments show that most of the electrons are emitted in the 125-375 keV energy range and the spectral amplitude becomes negligible beyond 375 keV.
文摘The Al/a-C nanocomposite thin films are synthesized on Si substrates using a dense plasma focus device with alu- minum fitted anode and operating with CH4/Ar admixture. X-ray diffractometer results confirm the formation of metallic crystalline Al phases using different numbers of focus shots. Raman analyses show the formation of D and G peaks for all thin film samples, confirming the presence of a-C in the nanocomposite thin films. The formation of Al/a-C nanocomposite thin films is further confirmed using X-ray photoelectron spectroscopy analysis. The scanning electron microscope results show that the deposited thin films consist of nanoparticles and their agglomerates. The sizes of th agglomerates increase with increasing numbers of focus deposition shots. The nanoindentation results show the variations in hardness and elastic modulus values of nanocomposite thin film with increasing the number of focus shots. Maximum values of hardness and elastic modulus of the composite thin film prepared using 20 focus shots are found to be about 10.7 GPa and 189.2 GPa, respectively.
基金This work was partially supported by Quaid-i-Azam University Research Grant, Ministry of Science & Technology Grant, Pakistan Science Foundation Project No. PSF/R&D/C-QU/Phys (199), Higher Education Commission Project for Plasma Physics, Pakistan Atomic
文摘Study on X-ray emission from a low energy (1.8 kJ) plasma focus devicepowered by a 9 μF capacitor bank, charged at 20 kV and giving peak discharge current of about 175kA by using a lead-inserted copper-tapered anode is reported. The X-ray yield in different energywindows is measured as a function of hydrogen filling pressure. The maximum yield in 4π-geometry isfound to be (27.3+-1.1) J and corresponding wall plug efficiency for X-ray generation is 1.52+-0.06%. X-ray emission, presumably due to bombarding activity of electrons in current sheath at theanode tip was dominant, which is confirmed by the pinhole images. The feasibility of the device asan intense X-ray source for radiography is demonstrated.
文摘The current sheath velocity in 0.25 Torr gas pressure of Filippov type plasma focus is studied experimentally. By using two tridimensional magnetic probes on top of the anode surface, the current sheath velocity is measured for argon, oxygen and nitrogen. Additionally, the effect of charging voltage on the current sheath velocity is studied in both axial and radial phases. We found that, the maximum current sheath velocities at both radial and axial phases are respectively 4.33 ± 0.28 （cm/μs） and 3.92 ± 0.75 （cm/μs） with argon as the working gas at 17 kV. Also, the minimum values of current sheath velocity are 1.48 ± 0.15 （cm/μs） at the radial phase and 1.14 ± 0.09 （cm/μs） at the axial phase with oxygen at 12 kV. The current sheath velocity at the radial phase is higher than that at the axial phase for all gases and voltages. In this study, variation of the full width half maximum （FWHM） of magnetic probe signals with voltage is investigated for different gases at radial and axial phases.
文摘A 2.3 kJ Mather type pulsed plasma focus device was used for the synthesis of a TiN/a-Si3N4 thin film at room temperature. The film was characterized using X-ray diffraction （XRD）, X-ray photoelectron spectroscopy （XPS）, scanning electron microscopy （SEM）, and atomic force microscopy （AFM）. The XRD pattern confirms the growth of polycrystalline TiN thin film. The XPS results indicate that the synthesized film is non-stoichiometric and contains titanium nitride, silicon nitride, and a phase of silicon oxy-nitride. The SEM and AFM results reveal that the surface of the synthesized film is quite smooth with 0.59 nm roughness （root-mean-square）.
基金supported partially by the Higher Education Commission Project for Plasma Physics of Pakistan
文摘A simple, low cost, easily maintained, and reliable field distortion spark gap has been developed to operate at a voltage up to 30 kV. The header construction necessary to attach the spark gap switch to a single 12.5 μF, 40 kV （10 k J） capacitor is described. The main features of the spark gap are its wide range of voltage operation, high current capacity, low inductance and long lifetime. The performance of spark gap has been tested in a plasma focus and results are presented in this report.
文摘The Al–C–N films are deposited on Si substrates by using a dense plasma focus（DPF） device with aluminum fitted central electrode（anode） and by operating the device with CH_4/N_2 gas admixture ratio of 1：1. XRD results verify the crystalline Al N（111） and Al_3CON（110） phase formation of the films deposited using multiple shots. The elemental compositions as well as chemical states of the deposited Al–C–N films are studied using XPS analysis, which affirm Al–N, C–C, and C–N bonding. The FESEM analysis reveals that the deposited films are composed of nanoparticles and nanoparticle agglomerates. The size of the agglomerates increases at a higher number of focus deposition shots for multiple shot depositions. Nanoindentation results reveal the variation in mechanical properties（nanohardness and elastic modulus）of Al–C–N films deposited with multiple shots. The highest values of nanohardness and elastic modulus are found to be about 11 and 185 GPa, respectively, for the film deposited with 30 focus deposition shots. The mechanical properties of the films deposited using multiple shots are related to the Al content and C–N bonding.
文摘Optimal condition for <sup>13</sup>N radioisotope production through <sup>12</sup>C (d,n) 13N within plasma focus device is investigated. As the deuteron spectrum follows the empirical power law of the form E<sup>-m</sup>, it is shown that the activity decreases by increasing the value of m. Unlike the fact that the repetition rate increases the activity, it is possible to achieve higher activities by increasing the bombardment time at a fixed repetition rate.
文摘In many experiments, plastic scintillators are used as a counter instead of Geiger Muller counter, because they are so fast and they are used for pulsed neutron sources. So a silver activation counter has been constructed by plastic scintillator plates along with silver foils for determination the neutron yield of a 2.48 kJ plasma focus device, SBUPF1. This counter was calibrated by source removal method with an Am-Be 5 Ci neutron source which was placed above the anode of plasma focus device. Deuterium gas up to 8 mbar pressure was injected to this device, and the neutron yield produced by pulsed D-D fusion of plasma focus device was measured by the counter. The neutron yield of SBUPF1 in 8 mbar pressure was obtained （3.71± 0.32）×10^7 neutrons per shot. This result has relatively agreed with the neutron yield measured by silver activation Geiger counters.
基金supported by the Ministry of Education,Science and Technological Development of Republic of Serbia under project OI171002.
文摘The plasma focus experiment in Belgrade, Serbia started in the late eighties of the last century. The historical overview of the research activity on the Belgrade plasma focus device (BPFD) will be presented in this work. The special attention has been made to the present status and the future plans for the fundamental and applied research as a part of the project of the studies of rare nuclear and particle processes in nature. BPFD is intended to operate as optimized neutron source or hard X-ray source. Using Lee model code as a reference, several upgrades of BPFD must be made: better shielding against EMI pulse, rearrangement of capacitors bank so that higher repetition rate can be achieved and also faster digital acquisition system. BPFD can be used for neutron activation or production of short-living radioisotopes. These radioisotopes will have very low activity which can be analyzed in the underground Low-Background Laboratory for Nuclear Physics, Zemun. Also, we compared the obtained experimental data (neutron yield, total current waveform, working gas pressure) with the numerical simulation code (The Lee model code) to test our plasma focus machine. Comparison between neutron yield from our experimental data and neutron scaling laws and neutron yields derived from computation using the Lee Model code shows good matching, but for better verification of the code, more experimental data are needed.
文摘In most collisional schemes of x-ray laser （XRL） experiments, a bow-like intensity distribution of XRL is often observed, and it is generally ascribed to the two-dimensional hydrodynamic behaviour of expanding plasma. In order to better understand its essence in physics, a newly developed two-dimensional non-equilibrium radiation hydrodynamic code XRL2D is used to simulate a quasi-steady state Ni-like Ag XRL experiment on ShenGuang-Ⅱfacility. The simulation results show that the bow-like distribution of Ni-like ions caused by over-ionization in the central area of plasma is responsible for the bow-like shape of the XRL intensity distribution observed.
文摘The Max’s equation of self-focusing in laser-plasma interaction due to the pondermotive force has been discussed and its physical meaning of the assumption has been predicted. The characteristics of selffocusing due to the pondermotive force with different initial situations have been analyzed through the numerical calculation.
基金suported by the National Natural Science Foundation of China (Grant No. 10874242)the National Basic Research Program of China (973 Program) (Grant No. 2007CB815105)Research Fund for the Doctoral Program of Higher Education of China (Grant No. 20070290008)
文摘Based on the two-dimensional model, this paper compares the hydrodynamics of slab x-ray laser plasma produced by different nonuniform line focused irradiations. It finds that the average intensity and the duration of laser pulse and the overall shape of the intensity distribution in the focal line have different influences on the plasma. Calculations show that the evolution of temperature variation is more sensitive to the pulse duration and the electron density variation is more sensitive to the pulse intensity. Pulses with duration of 200 ps to 500 ps and with intensity of 0.2 TW/cm2 to 1.0 TW/cm2 are proved acceptable in slab x-ray lasers.
